Process for metal finishing boron and tungsten filaments



R. L. HOUGH Nov. 12, 1968 PROCESS FOR METAL FINISHNG BORON AND TUNGSTEN FILAMENT 2 Sheets-Sheet 1 Filed June 28, 1965 Ru Q a, J a

INVENTOR 0!!! 1. #0066 A'rfoRN PROCESS FOR METAL FINISHNG BORON AND TUNGSTEN FILAMENTS Filed June 28, 1965 2 Sheets-Sheet 2 as 32 m 'IIIIIIIIIIJ j 2 25 28 Z 3 II/II/I/I/I/A 29* 8 V INVENTOR amp/: 4- #0067! United States Patent PROCESS FOR METAL FINISHING BORON AND TUNGSTEN FILAMENTS Ralph L. Hough, Springfield, Ohio, assignor to the United States of America as represented by the Secretary of the Air Force Filed June 28, 1965, Ser. No. 467,792 Claims. (Cl. 117-71) ABSTRACT OF THE DISCLOSURE A process for applying an aluminum finish to boron and boron coated tungsten filaments. The filaments are heated to within the range of 1800 F. to 2100" F. and then passed through molten aluminum in an inert atmosphere whereby an aluminum boride layer is formed betweenthe filament and the aluminum coat.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a new and improved process for applying a metal finish to boron filaments, to a process for combining filaments into ribbons and cables, and to the products so made.

Filaments have been made and used previously as reinforcements for matrix materials. Boron filaments have commonly been characterized by defective surfaces. The filament surfaces of prior filaments have lacked dependable bonding with the matrix in which they have been imbedded and have not exhibited uniform mechanical properties, strengths and resistances to deterioration.

The objects of the present invention are to provide a new and improved process for applying metal finishes to boron filaments and for grouping the filaments in the making of ribbons, cables and the like. The improved filaments are made by a process that is admirably adapted for automatic, continuous, and endless production. The improved filaments may be used to strengthen composites of the filaments with metals, ceramics, plastic resins and the like.

In the accompanying drawings:

FIG. 1 is a diagrammatic illustration of 'an apparatus usable in the practice of the present invention;

FIG. 2 is a modification of the apparatus in FIG. 1;

FIG. 3 is a diagrammatic illustration of an apparatus for combining desired groups of filaments into ribbons and cables; and

FIG. 4 are sectional views of simple and complex filaments grouped into ribbons in A and B and into cables in- C and D, with enlarged sections to the right thereof.

In FIG. 1 of the accompanying drawings, a boron filament 1 is passed from a supply spool 2 through minimum size holes in the ends of a furnace 3 to a collecting or storage spool 4. The interior of the furnace 3 is provided with an atmosphere of an inert gas, such as argon, that is maintained substantially pure by adjusting its pressure from its source 5 at slightly above ambient.

Within the furnace 3 the temperature of the filament 1 is maintained about within the range of from 1800-2100 F. by the application of an electromotive force E across the filament 1 between a filament wiping contact 6 and a graphite pot 7. The graphite pot 7 contains aluminum in its molten state. A resistance winding 8 maintains the temperature of the graphite pot 7 about within the range of from 1220-1300 F. Within this temperature range, the surface of the boron filament is at least infinitesimally reacted with aluminum to form aluminum boride that bonds the aluminum to the filament.

The aluminum boride so formed is a chemical reaction product between the boron and the molten aluminum in an inert atmosphere. The quenching from a higher temperature of the boron filament plunged into the lower temperature molten aluminum is important in accomplishing the formation of aluminum boride on the surface of the boron filament. The depth of the aluminum boride is controlled at least in part by the dwell time of the boron filament in the molten aluminum and by a desired repetition of this immersion.

The aluminum boride is integrally attached to, and is chemically combined with, the boron filament such that the aluminum coating that is picked up by the boron filament on passing through the molten aluminum within the pot 7, is of a controlled thickness and has passed to its solid state prior to its being wound on the storage spool 4.

In a first specific embodiment of the invention, the boron filament 1 has a diameter of about 2.0 to 2.2 mils. The boron filament was resistance heated in argon to 1800-2100 F. The boron filament at this temperature is then drawn into the bath of molten aluminum within the pot 7 which is held within the temperature range of between l2201300 F. The illustrative velocity of drawing the boron filament through the molten aluminum is about 2 feet per minute. This velocity may be increased or decreased as preferred. A tightly adherent and very uniform coating of aluminum on the boron filament was obtained over a total length of 700 feet. The range of thickness of the aluminum coating on the boron filament was about from 25 microns.

In a second specific embodiment of the present inven tion, the metallized boron filament so produced was wound together with a single strand of aluminum wire of 2.2 mils diameter, on a spool that was 2 feet in circumference. After the aluminum finished boron filament supply was exhausted, the resulting yarn was cut from the spool in one foot lengths. Graphite hand grips were applied to each end of the experimental one foot lengths to the yarn. The lengths of yarn were placed under slight tension in a mufile furnace provided with an argon atmosphere. The experimental one foot lengths of the aluminum finished boron filament and single strand aluminum wire yarn were annealed in a mufile furnace argon atmosphere at about l220-1300 F. for a few minutes to permit the aluminum wide component of the yarn to melt and to thoroughly infuse the metallized boron filaments. The resulting composite was then allowed to solidify in argon and was withdrawn from the furnace.

The apparatus in FIG. 2 of the drawings is used to provide a tungsten filament that is clad with a surface coat of aluminum with boron therebetween.

In FIG. 2 a tungsten filament 10 is passed from a supply spool 11 through minimum size apertures in the ends of the furnace 12 to a storage spool 13 as an aluminum boride and aluminum-coated tungsten filament.

The interior of the furnace 12 is divided by a partition 14 into a boron plating chamber and an aluminum-boron alloying chamber. The partition 14 is apertured with a minimum size hole for the passage of the filament 10 through the partition. The boron-on-tungsten filament coating chamber on the upstream side of the partition 14 is supplied a flow of a boron plating gas, indicated by MB(v), between the fittings 16 and 17 at a controlled pressure. The gas that is illustrated by the symbol MB (v) illustratively may have the composition boron trihalide mixed with hydrogen.

On the downstream side of the partition 14 the tungsten filament coated with a layer of boron passes through molten aluminum in a graphite crucible or pot 15, thereby changing the surface of the boron coat on the tungsten filament to AlB The fitting 18 supplies argon gas at a pressure slightly above ambient to the aluminum-boride coating chamber on the downstream side of the partition 14. The electrical potential E is applied to resistance heat the tungsten filament continuously between the filament wiping electrical contact 19 and the pot 15 at a temperature in the range of from 18002100 F., and to coat continuously the filament with boron. The pot is maintained at a temperature within about the range of from 12201300 F. by the resistance winding 20. As the hot filament is drawn into the relatively cool molten aluminum, the filament is quenched to the aluminum bath temperature as an infinitesimal metallurgical bond by thermal diffusion at the higher filament temperature.

The filament emerging from the molten-aluminum bath is uniformly coated with a thin, tightly adherent finish of aluminum metal. For additional thicknesses of the aluminum coating on the filament, the filament is caused to make a desired number of repeated passes through the molten aluminum within the pot 15.

In FIG. 3 of the drawings, a desired plurality of filaments are fed simultaneously into a furnace. Illustratively, a supply spool 25 provides an aluminum filament 26 and a supply spool 27 provides a composite filament 28, such as the previously described filament consisting of a tungsten core, surfaced with aluminum, bonded by a layer of aluminum diboride, or the like.

The plurality of filaments are gathered into a desired grouping by suitable means, such as between the pair of engaging rolls 29, 29', etc., shown in FIG. 3 of the drawing. A plurality of filaments so grouped are passed through the furnace 30 and are wound upon the collection or storage spool 31. The furnace 30 is maintained at a desired temperature by suitable means, such as by the resistance winding 32, or the like. The atmosphere within the furnace is maintained inert in a suitable manner as by passing argon or the like, between the fittings 33 and 34. The temperature within the furnace 30 may be maintained at about the melting point of aluminum. The filament travel rate through the furnace is adjusted such that surface bonding between adjacent filaments occurs without objectionable deformation of the end product.

Representative aggregate filament forms are illustrated in sectional views, such as the ribbon structures in FIG. 4, sectional views A and B, and as cables in FIG. 4, sectional views C and D.

In FIG. 4 are shown in cross-sectional views, illustrative groupings of the filaments that are made by the use of the apparatus that is described herein, and that are grouped in a desired association by the use of the apparatus that is illustrated in FIG. 3.

In FIG. 4A, a plurality of filaments of desired compositions are fed from the supply spools 25, 27, etc., to between the cylindrical rolls 29, 29, etc., that are of a length somewhat longer than the width of the ribbon to be made. The filaments in juxtaposition within the furnace 30 are subjected to temperatures at which the metallized boron filaments and the lower metal temperature metal filaments are surface bonded together by incipient fusion as a continuous ribbon 35.

The ribbon 35 product may be annealed in an inert atmosphere in a muffie furnace, or by electrical resistance heating in an inert atmosphere, or the like, not shown. The ribbon 35 so made as illustrated in enlarged section A to the right of FIG. 4A may consist of aluminum filaments 36, 36', etc., alternated with filaments of more composite desired structures, such as the aluminum filament 37 that consists of a tungsten core coated with boron surfaced with aluminum; the filament 38 that consists of a tungsten core coated with aluminum surfaced with aluminum diboride, and the like.

In FIG. 4B is shown cross-sectional views of a ribbon 40 that consists of boron filaments 41, 41', etc., that are surfaced with aluminum 42. The enlargement B indicates aluminum diboride 43 on the filament surfaces. The filaments are aligned and are fed between the cylindrical rolls 29 and 29' to the furnace 30 that is held at a temperature that fluxes the aluminum without melting the boron. The annealing of the ribbon accomplishes the finished product.

The FIG. 4 sectional views C and D are cables 45 and 46, respectively, that are made by feeding a desired plurality of filaments from the supply spools 25 and 27 to pairs of mating, concave, semispherically grooved section rolls, not shown, from which the cables are passed through the furnace 30, annealed and are fed to the storage spool 31.

A hollow lance made of graphite, not shown, may if preferred be used as a filament, ribbon or a cable travel guide for passage through the furnaces that are disclosed herein. The lance may serve to admit a pre-arrayed geometry of aluminized boron fibers below the surface of an aluminum melt, without danger of contacting surface aluminum oxide, said oxide causing serious detriment to the integrity of the finished product.

It is to be understood that the filaments, compositions, furnaces and processes that are disclosed herein are submitted as being illustrative, successfully operating constructive reductions to practice of the present invention and that modifications may be made therein without departing from the present invention.

I claim:

1. The filament metal finishing process comprising passing a boron filament to an inert gas containing enclosure, heating the boron filament to within about the range of 1800 F. to 2100 F., immersing the heated boron filament in molten aluminum, and at least infinitesimally reacting the surface of the boron filament with the molten aluminum to form an integrally attached chemically combined bond between the boron and the aluminum.

2. The process defined by claim 1 together with the further step of repeating the passage of the aluminum surfaced boron filament through the molten aluminum for increasing the thickness of the aluminum coat.

3. The process of metal finishing a tungsten filament with layers of boron and aluminum by passing the tungsten filament into a boron vapor atmosphere, increasing the temperature of the tungsten filament in the boron vapor atmosphere to about the range of from 1800 F. to 2100 F., passing the boron coated tungsten filament through molten aluminum, and permitting the solidification of the boron and aluminum on the surface of the tungsten filament.

4. The metal finished boron filament comprising a boron filament, a surface coat of at least an infinitesimal aluminum diboride coat on the surface of the boron filament, and an aluminum coat on the surface of the boron filament with the aluminum diboride coat interposed between the boron filament and the aluminum coat.

5. The metal finished tungsten filament comprising a tungsten filament, a boron coat bonded to the surface of the tungsten filament, and at least an infinitesimal coat of aluminum boride on the boron coat on the tungsten filament, and a coat of aluminum on the aluminum boride coat on the tungsten filament.

References Cited UNITED STATES PATENTS 2,849,336 8/1958 Reid et al. I1771 X 2,970,068 1/1961 Drummond 117-71 3,057,050 10/1962 Hodge et al. 1171l4 RALPH S. KENDALL, Primary Examiner. C. K. WEIFFENBACH, Assistant Examiner. 

